Power supply management is a significant challenge in terminal and smart sensor design. This is because such terminals and sensors typically have a limited battery capacity. Anything that can be done to reduce power consumption for such wireless terminals and sensors would be of benefit.
Traditional terminal/receiver designs drain a large amount of power even if the terminal is in an idle or dormant mode. The reason for this is that the terminals are required to monitor a paging channel or a beacon channel all the time.
OFDM (orthogonal frequency division multiplexing) terminals typically drain even more power than CDMA/TDMA (code division multiple access/time division multiple access) terminals due to the fact that such terminals run their wide band and high resolution ADC (analog-to-digital converter) and FFT (Fast Fourier Transform)/sub-FFT engines all the time, or at least during any period that detection of any signals is to be possible.
For example, an OFDM terminal in sleep mode will typically periodically wake up to see if it has any messages. However, conventional terminals must perform processing on the full OFDM bandwidth to see if there are any messages. This takes a significant amount of power because a full analog-to-digital conversion on the entire bandwidth of the OFDM system must be performed together with the processing of the whole digitized data block in terms of data buffering, framing, full FFT computation etc. Typically, the paging channel is transmitted at a particular time and frequency with the same processing engine as the main task channels and the terminal must wake up in order to look at the paging channel.
It is also noted that due to the high peak-to-average power ratio, the ADC needs to cover a high dynamic range, and this also increases the power consumption.